Sequential single pion production explaining the dibaryon "$d^{\ast }(2380)$" peak

Abstract

We study the two step sequential one pion production mechanism, $np(I=0)\to \ddot{I}{€}^{-}pp$, followed by the fusion reaction $pp\to \ddot{I}{€}^{+}d$, in order to describe the $np\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}d$ reaction with $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ in $I=0$, where a narrow peak, so far identified with a "$d(2380)$" dibaryon, has been observed. We find that the second step $pp\to \ddot{I}{€}^{+}d$ is driven by a triangle singularity that determines the position of the peak of the reaction and the large strength of the cross section. The combined cross section of these two mechanisms produce a narrow peak with the position, width and strength compatible with the experimental observation within the approximations done. This novel interpretation of the peak without invoking a dibaryon explains why the peak is not observed in other reactions where it has been searched for.

6 pages, 2 figures, 1 table